Processing titanium alloy sheet products



United States Patent 3,333,995 PROCESSING TITANIUM ALLOY SHEET PRODUCTS Harry W. Rosenberg, Henderson, Nev., and Eugene F. Erbin, Chatham, N.J., assignors to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 5, 1963, Ser. No. 328,208 8 Claims. (Cl. 148131) This invention relates to processing titanium base alloy sheet products, and more particularly to flattening and heat treating such products of substantially alpha-type titanium base alloys to impart enhanced toughness, as well as flatness.

Alpha-type titanium base alloys, particularly those containing aluminum as an alpha stabilizer, are light, strong and ductile and find applications in sheet form in the aeronautical and missile arts. They find use in manufacture of jet engines and airframes, as well as missile and rocket components. Many of these applications require toughness as well as flatness in the alloy sheets.

Flatness is often obtained in titanium alloy sheets by use of what is known in the art as a car-bottom anneal, followed by furnace cool. This provides acceptable flatness in the sheet product but its toughness, measured by sharp notch tensile strength, is adversely affected.

Summarized briefly, this invention provides a heat treatment to improve toughness of certain types of alpha-type titanium base alloys in sheet form; this heat treatment being employed in combination with a so-called car-bottom anneal employed previously to flatten the sheets. The car-botton anneal comprises piling a number of alloy sheets, one on top of another inthe flat bottom of a movable car. Such sheets may vary from say 0.020 to 0.120 inch in thickness and the load of total number of such sheets piled in the car bottom will naturally depend on the nature and size of the equipment. On top of the pile of sheets is placed a load plate, which may be a heavy steel plate, to provide a uniform load on top of the sheet pile. The load may, for example, be of the order of two pounds per square inch. The car, with its load of piled sheets and the load plate, is then wheeled into the furnace whose interior is provided with an inert atmosphere, for example of argon. The sheets are heated in the furnace in place in the car for from 4 to 12 hours at a temperature from 1325 to 1475 F. The furnace is then allowed to cool and the temperature of the sheets will drop slowly, often taking as long as 15 to 20 hours to drop to a temperature at which the sheets may safely be exposed to the atmosphere. This may be below 1000 F. and preferably below 600 F. The heating and slow cooling under flattening load pro vides sheets of acceptable flatness, for example, less than 3% flatness by a test described in more detail hereinafter. The heat treatment comprises heating the sheet product after flattening at a temperature of from 1350 to 1400 F.

for at least 5 minutes, and preferably from 5 to 20 minutes, and subsequently cooling the sheet product so that its passage through the range of 1200 to 1000 F. is accomplished in less than one hour. The sheet product may be air cooled which will provide a sufiiciently rapid cooling through the critical range; or may be quenched, as by immersion in Water or oil, which will provide extremely rapid cooling to normal or room temperature in a matter of seconds or at most a few minutes.

The titanium base alloy of which the sheet product is fabricated is of the all-alpha or substantially all-alpha type. The alloy will contain aluminum in amount from 5% to 8.5%. Less than 5% will not provide the advantageous strengthening effect of the aluminum content and over 8.5% will result in a tendency towards brittleness in the alloy. Tin may be present in amount up to 6% and zirconium in amount up to 9%. Oxygen may be present in amount from 0.05% to 0.2%. We have found that the alpha strengthening effect of tin, zirconium and oxygen is roughly one-third, one-sixth and ten times, respectively, of the effect shown by aluminum. Therefore, tin, zirconium and oxygen as alpha stabilizers may replace aluminum so that 3% of tin may replace 1% of aluminum, 6% of zirconium may replace 1% of aluminum and 0.1% of oxygen may replace 1% of aluminum. The aluminum equivalent calculated on the basis of percent aluminum plus one-third the percent of tin plus one-sixth the percent of zirconium plus ten times the percent oxygen should be between 7% and 9% in the alloy to provide the desired proportion of alpha stabilizers to give characteristics of increased strength and low specific gravity. To provide additional strength without adversely affecting ductility,

up to 3% of beta isomorphous elements columbium, tantalum, molybdenum and vanadium may, under certain conditions, advantageously be included. We have found that up to 3% of such elements will improve strength and also provide some degree of heat treatability without destroying the essentially all-alpha characteristics of the alloy. The beta stabilizer may be any of these elements individually or may be combinations of them so long as the total does not exceed 3 Alloys of which the sheet product according to this invention may be fabricated may include, but not be limted to, the following examples listed in Table 1.

TABLE 1 5% Al2.5% Sn0.17% O balance Ti The balance of the alloy will be titanium and incidental impurities. Incidental impurities will ordinarily be present in titanium sponge employed to produce the alloy and in the alloy elements themselves or in master alloys composed of a plurality of or combination of such alloy elements. Incidental impurties may also be picked up to some extent by titanium and its alloys during processing. The total amount of such incidental impurities should not exceed about 0.4% of which the interstitials nitrogen and carbon should not exceed about 0.15%

The heat treatment of this invention comprises heating flattened sheet products fabricated of the alpha-type titanium base alloy described above at a temperature of from 1350 to 1400" F. Preferably, the heating is at 1375 F. to provide best results. We have found that heating at temperatures above 1400 F. is not required to provide optimum toughness, and a higher temperature tends to degrade the product by surface oxidation. Heating a product of the alpha-type titanium base alloy at temperatures below 1350 F. for any appreciable length of time will result in a serious loss of toughness. This effect is so marked that when cooling from the heating range of this invention, the transition through lower temperatures, particularly between 1200 and 1000 F., should be as rapid as possible and in all cases less than one hour.

The time of heating the sheet product according to this invention is important. A period of at least 5 minutes at a temperature of from 1350 to 1400 F., and preferably at 1375 R, will insure that adequate heat has been applied to attain the required metallurgical conditions. No harm will ordinarily occur as a result of heating for substantially longer time if the heating furnace is provided with an inert atmosphere to prevent deleterious oxidation by atmospheric contamination.

result of uneven quenching.

alloys listed in Table 1.

Time at temperature should be long enough to insure required creep flattening effect and this will generally be up to about 8 hours or longer. Excess time at temperature, that is longer than about 8 hours, will not ordinarily provide additional benefits, though it will do no harm. or contamination of the product surface. For furnaces in Such excess time will, of course, add to annealing expense. which no special atmosphere is employed, the time at tem- Cooling of the creep flattened sheets must be done perature should be from 5 to 20 minutes and not longer to slowly and the precise convenient rate will often depend avoid surface deterioration. Times in the upper part of on equipment capabilities. The flattened sheets should be this range, that is from 15 to 20 minutes, are useful to pro- 10 cooled in the furnace from annealing temperature down to vide suflicient soaking so that temperature effects on metal- 1000 F. or preferably 600 F. in not less than 10 hours, lurgical structure will be unquestionably uniform. A preand hours will be preferred. The sheets should not be ferred time is about 15 minutes which provides adequate removed from the inert atmosphere of the furnace before time at temperature without risking surface degradation they have been cooled sufficiently to be safely exposed 15 to air. This can be accomplished at 600 F., and even The rate of cooling the heat treated product is an imas high as 1000 F. with slight surface degradation. Such portant aspect of this invention. It is essential that the processing should produce sheet with average flatness of hot product be cooled through the range between 1200 less than 3% with this determined as follows: A long and 1000 F. in less than one hour. We have found that straight edge is laid in various longitudinal and transverse retention for more than an hour within this critical tempositions across the sheet. The height of the valleys or deperature range will adversely affect toughness properties. pressions from their bottoms to the straight edge is meas- Therefore, to obtain the highly desirable toughness charured as well as the distance between high points on either acteristic, the product is cooled relatively rapidly from its side of such valleys or depressions. The average of valley heat treating temperature to ordinary or room temperature height divided by high point distance times 100 will give by any method that will insure that the cooling between' percent flatness. For example, a depression measured 0.2 1200 and 1000 F. is less than one hour. This may be acinch from its bottom to a straight edge laid across the complished by a process known in the art as air cooling sheet. High points on either side of the sheet touching the in which the hot product is removed from the heat treating straight edge were 10 inches apart. Flatness would be caland allowed to cool in the open air. The loss of heat in culated as 2%. air cooling will be such that the cooling within the critical Table 3 below provides, as an example of the practice range of 1200 to 1000 P. will be safely greater than 200 of this invention, sharp notch tensile strength test results F. per hour. For flat rolled products such as sheet, air on an alloy consisting essentially of 8% aluminum, 0.08% cooling is generally more desirable than quenching since oxygen, 1% molybdenum, 1% vanadium, balance titadimensions of sheet make it difficult as a practical matter nium and incidental impurities. Sheet fabricated from this to apply a uniform quench, and buckling, oil canning or alloy was flattened by employing a car-bottom anneal. A other distortion may occur in commercial size sheet as a number of sheets were stacked one on top of another and a heavy load plate weighing about two pounds per square The car-bottom anneal may be considered to be creep inch was placed on top of the sheet stack. The assembly flattening, the sheets being heated and maintained under was wheeled into a furnace in the bottom of a car and load for a suflicient time for plastic deformation to have the furnace provided with an interior atmosphere of argon. occurred to flatten irregularities in the original sheet. As The furnace interior was heated until the sheet stack had previously discussed, the flattening step of this invention attained a temperature of 1450 F. and this temperature should be carried out at temperatures of between 1325 was maintained (plus or minus 15F.) for a period of 8 and 1475 F. for from 4 to 12 hours, preferably about 8 hours. The furnace was then allowed to slowly cool and hours. Within this range, alloys that are characteristically after 10 additional hours, the furnace interior and its more creep resistant will require higher temperatures for contents had cooled to 600 F. The sheets were then reeflicient flattening under similar time and load conditions. moved from the furnace, cooled to ambient temperature The following table shows the 8-hour car-bottom annealand tested for flatness and notch tensile strength. ing temperature preferred for each of the representative After flattening, sheets were heated at 1375 F. for 15 minutes and were air cooled.

TABLE 3 Sharp Flatness, Notch Alloy Processing Percent Tensile Strength, p.s.i.

Ti-8 Al-1 Mo1 V, Heat D-1237 1,450 F., 8 Hrs, Car-bottom anneal, Furnance Cooled 3 85, 400 Do- Same as above plus heating to 1,375 F., 15 Min., Air 0001... 3 127, 000

1 K.=17, where K. relates to the severity of the stress concentration. Higher values indicate greater sharpness or acuity of the notch.

TABLE 2 F. Ti5% Al-2.5% Sn0.17% O 1450:25 Ti8% Al0.08% O 1% Mo-1% V 1450:15 Ti7 %Al0.08% O 2% Cb1% Ta 1350:25 Ti5% Al5% Sn5% Zr0.1% O 1350125 Ti6% Al-2% Sn-2% ZrO.12%

o 1% Mo 1450:15 Ti6% Al3% Sn9% Zr0.07% O 1350:25

Mo-1%V 1450:25 75 Data is shown in Table 4 for specimens of flattened sheets heated at 1375 F. and Water quenched and then held for various periods of time within 900 F. to 1200 F. It will be seen that when processed according to this invention, sharp notch tensile strength of 130,000 p.s.i. was obtained compared to from 105,000 to 110,000 p.s.i. when the product was held in the 900 to 1200 F. temperature range.

While specific data has been shown in Table 3 for a Ti8 Al-1 Mo-l V type alloy, the same effect and trend will be obtained as a result of similarly processing other alpha-type titanium alloys within the composition ranges hereinbefore described. The actual notch tensile strength values will vary somewhat with various alloy ingredients and the flatness obtained in a uniform car-bottom anneal processing step will be somewhat less for those alloys having higher creep strength. Flatness and sharp notch tensile strengths which will be found representative for the other alloys listed in Table l are shown in Table 5 below.

The alhpa-type titanium base alloys to be processed by the method of this invention may be produced by any method by which the titanium and alloying elements are melted together to form a substantially homogeneous alloy composition. Preferably, titanium sponge of required purity and particularly with respect to its oxygen content, is admixed with subdivided alloying elements in proper amounts and the mixture compressed into compacts. Alternatively if desired or more convenient, the required oxygen content of the alloy may be obtained by incorporating an oxygen-containing compound such as TiO into the compact mixture, After pressing the mixture into compacts, these are welded together to form an elec trode which may be melted in a consumable electrode arc melting furnace to produce an ingot of alloy. The soproduced alloy ingot may itself be employed as an electrode in a subsequent remelting ste to provide homogeneity in a final alloy ingot.

The alloy ingot may be handled in the mill by conventional procedures to produce sheet. It may, for example, be forged to a suitable billet which is then rolled to sheet bar and subsequently rolled to sheet of desired Width, thickness and length.

The sheet products processed according to this invention will possess, among other desirable mechanical properties, a combination of flatness and good toughness measured conveniently as sharp notch tensile strength. Such properties make the flattened and heat treated sheet useful in the aeronautical and missile arts as well as for use in the manufacture of jet engines, airframes and other applications where light weight, strength, flatness and toughness are particularly desirable.

We claimt 1. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05 to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbiurn, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for from 4 to 12 hours followed by furnace cooling, and

(b) subsequently heating said flattened sheet product at a temperature of from 1350 F. to 1400 F, for .at least 5 minutes and cooling said sheet product to room temperature at a rate such that the cooling from 1200 F. to 1000 F. is accomplished in less than one hour.

2. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5 aluminum, up to 6% tin, up to 9% zirconium, from 0.05 to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus one-sixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for about 8 hours followed by furnace cooling for a period of about 10 hours, and,

(b) subsequently heating said flattened sheet product at a temperature of from 1350 F. to 1400 F. for at least 5 minutes and cooling said sheet product to room temperature at a rate such that the cooling from 1200 F. to 1000 F. is accomplished in less than one hour.

3. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05% to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for about 8 hours followed by furnace cooling to about 600 F. over a period of at least 1-0 hours, and,

(b) subsequently heating said flattened sheet product product at a temperature of from 1350 F. to 1400 F. for at least 5 minutes and cooling said sheet product to room temperature at a rate such that the cooling from 1200 F. to 1000" F. is accomplished in less than one hour.

4. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05% to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for from 4 to 12 hours followed by furnace cooling, and,

('b) subsequently heating said flattened sheet product at a temperature of from 1350 F. to 1400 F. for a period of from 5 to 20 minutes and cooling said sheet product to room temperature at a rate such that the cooling from 1200 F. to 1000 F. is accomplished in less than one hour.

5. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05% to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for from 4 to 12 hours follower by furnace cooling, and,

(b) subsequently heating said flattened sheet product at a temperature of about 1375 F. for a period of about 15 minutes and cooling said sheet product to room temperature at a rate such that the cooling from 1200" F. to 1000 F. is accomplished in less than one hour.

6. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05% to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for from 4 to 12 hours followed by furnace cooling, and,

(b) subsequently heating said flattened sheet product at a temperature of from 1350 F. to 1400 F. for a period of from 5 to 20 minutes and air cooling said sheet product to room temperature.

7. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight from 5% to 8.5% aluminum, up to 6% tin, up to 9% zirconium, from 0.05 to 0.2% oxygen, with the sum of the percent aluminum plus one-third the percent tin .plus onesixth the percent zirconium plus ten times the percent oxygen being between 7% and 9%, and up to 3% of beta stabilizer selected from the group consisting of columbium, tantalum, molybdenum, vanadium, and combinations thereof, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature from 1325 F. to 1475 F. for from 4 to 12 hours followed by furnace cooling, and,

(b) subsequently heating said flattened sheet product at a temperature of from 1350 F. to 1400 F. for a period of from 5 to 20 minutes and quenching said sheet product to room temperature.

8. A method for processing a sheet product fabricated from an alloy consisting essentially of by weight about 8% aluminum, about 1% molybdenum, about 1% vanadium, about 0.08% oxygen, with the balance titanium and incidental impurities, which comprises:

(a) creep flattening said sheet product in an inert atmosphere in a furnace under load at a temperature of about 1450 F. for about 8 hours followed by furnace cooling, and,

(b) subsequently heating said flattened sheet at a temperature of about 1375 F. for a period of about 15 minutes and air cooling said sheet product to room temperature.

No references cited.

DAVID L. RECK, Primary Examiner.

H. F. SAITO, Assistant Examiner. 

1. A METHOD FOR PROCESSING A SHEET PRODUCT FABRICATED FROM AN ALLOY CONSISTING ESSENTIALLY OF BY WEIGHT FROM 5% TO 8.5% ALUMINUM, UP TO 6% TIN, UP TO 9% ZIRCONIUM, FROM 0.05% TO 0.2% OXYGEN, WITH THE SUM OF THE PERCENT ALUMINUM PLUS ONE-THIRD THE PERCENT TIN PLUS ONESIXTH THE PERCENT ZIRCONIUM PLUS TEN TIMES THE PERCENT OXYGEN BEING BETWEEN 7% AND 9%, AND UP TO 3% OF BETA STABILIZER SELECTED FROM THE GROUP CONSISTING OF COLUMBIUM, TANTALULM, MOLYBDENUM, VANADIUM, AND COMBINATIONS THEREOF, WITH THE BALANCE TITANIUM AND INCIDENTAL IMPURITIES, WHICH COMPRISES: (A) CREEP FLATTENING SAID SHEET PRODUCT IN AN INERT ATMOSPHERE IN A FURNACE UNDER LOAD AT A TEMPERATURE FROM 1325*F. TO 1475*F. FOR FROM 4 TO 12 HOURS FOLLOWED BY FURNACE COOLING, AND (B) SUBSEQUENTLY HEATING SAID FLATTENED SHEET PRODUCT AT A TEMPERATURE OF FROM 1350*F. TO 1400*F. FOR AT LEAST 5 MINUTES AND COOLING SAID SHEET PRODUCT TO ROOM TEMPERATURE AT A RATE SUCH THAT THE COOLING FROM 1200*F. TO 1000*F. IS ACCOMPLISHED IN LESS THAN ONE HOUR. 